Cytokinins are hormones that promote cell division and differentiation in plants. Most research into cytokinin biochemistry has focused on purine-derived cytokinins. These molecules are synthesized and metabolized naturally in plant tissue and target genes affecting the cell cycle and shoot meristem formation. Less understood are phenylurea-derived cytokinins, which can be synthesized in a laboratory and applied to plants exogenously. Since their discovery just over half a century ago, phenylurea-derived cytokinins have been shown to possess many of the same properties as purine-derived cytokinins, and have been used to promote plant growth in agriculture.
Forchlorfenuron (CPPU) is a phenylurea-derived cytokinin that has entered widespread use in the United States in the last ten years. Forchlorfenuron acts synergistically with natural auxins to promote lateral growth, and has been used to improve fruit size, fruit set, cluster weight and cold storage in grapes and kiwifruits. These growth enhancements have generally resulted from application of forchlorfenuron to plants at post-bloom growth stages, directly to flowers or developing fruit. There is scope to treat plants, particularly annuals and biennials, with forchlorfenuron at earlier growth stages and using different methods, and such treatments have the potential to affect growth more broadly. There is also a need for novel treatments that enhance root growth. Surprisingly, the present invention meets this and other needs.